Gravitational Lens

Two very close quasistellar objects (now called quasars) were discovered in 1979 with nearly identical spectral characteristics. Astronomers assumed their initial conditions must be similar, but found that they were in fact two images of the same object produced by a gravitational lens. Observations were made using the KPNO 2.1-meter Telescope and UArizona Bok 2.3-meter Telescope at Kitt Peak National Observatory.